Impending Friction vs nonimpending?

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SUMMARY

This discussion focuses on understanding impending friction in mechanical systems, particularly when analyzing equilibrium equations. It highlights that the frictional force can be calculated using the static friction coefficient (Us) only when impending motion is present. The conversation emphasizes that a block at rest on a horizontal surface does not exhibit impending motion, while the same block on an inclined plane does, indicating that impending motion refers to the condition just before slipping occurs. The transition from static to kinetic friction is also noted, where the coefficient of static friction is replaced by the coefficient of kinetic friction once motion begins.

PREREQUISITES
  • Understanding of static and kinetic friction coefficients
  • Knowledge of equilibrium equations in mechanics
  • Familiarity with the concepts of normal force and gravitational force
  • Basic principles of inclined planes in physics
NEXT STEPS
  • Study the differences between static and kinetic friction coefficients
  • Learn about equilibrium conditions in mechanical systems
  • Explore the effects of inclined planes on frictional forces
  • Investigate real-world applications of impending motion in engineering
USEFUL FOR

Students of physics, mechanical engineers, and anyone interested in the principles of friction and motion in mechanical systems will benefit from this discussion.

CProgWiz
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Hi all,

How do you know if friction is impending in a system?

I'm working on some problems, and in textbooks it tells you when you're dealing with equilibrium equations, sometimes you can consider Frictional force = (Us) * Force normal...

Next it says you can only consider that if there is impending motion. Then it says with no apparent impending motion, you can't use this... But it doesn't specify how you would know whether or not it is impending? Many of the problems seem very similar..

Thanks
 
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One (obvious) case is:

A block at rest on a horizontal surface has no tendency to move.
But it WILL have a tendency to slide if the same block is on an inclined plane.
 
I think "impending" would mean that something is about to slip.
As soon as it starts to slip, the coefficient of static friction
needs to be replaced by the (smaller) coefficient of moving friction.

As you tilt the block ,as described by grzz, the resisting frictional
force increases to exactly counter the resolved component of
gravitational force along the block. And, of course, the normal (at
right angle) reaction of the slope against the block also lessens -
with an effect on the realisable frictional force.
 

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